In this tech-demo, the Keystone cop runs along a train. The background has parallax scrolling to simulate movement, but it's still a flip-screen game. While the graphics are outstanding no game play elements have been implemented in this version of the prototype.

From AtariMania:

Also known as Keystone Cannonball.

According to programmer Dan Kitchen: 'I had also done a sequel to Keystone Kapers, which was the Keystone cop on a train. And that was actually a neat thing because I was able to pull off some interesting software kernels where I had eight rotating wheels on the bottom of a train where you could normally only have 2 or 6. It was a very cute game. From screen to screen, from boxcar to boxcar fighting and trying to defeat the character from Keystone Kapers, who was the runaway criminal. That was a very huge game as it had non-symmetrical play and had a really nice, large engine at the front of the game and a very large caboose at the bottom of the game.'

Of course, it's impossible to determine whether or not this would have been a worthy sequel to a really good game. But going by the video of the tech demo of the game posted on You Tube, it looked very promising. It's such a shame that it was never finished or released worldwide...